In the context of clinical chemical analysis methods, diagnosis test strips have gained more and more importance in recent years. The developments of recent years concentrate, above all, on the following aims:
1) improving the accuracy and reliability so that results of the quality of conventional wet chemical methods can be achieved. It was possible here to achieve enormous advances using plastic matrices, which can be produced with high uniformity, in combination with reflectometric analysis methods. PA0 2) expanding the test range from glucose to other analytes in blood and urine including immunodiagnostic detection reactions, and PA0 3) a test procedure which is as straightforward as possible, which in the ideal case is restricted only to sample application. Handling-independent test systems of this type, frequently also called technique-independent in English usage, are an important advantage compared with the conventional wipe-off test strips, especially for self-diagnosis by untrained patients.
To achieve the property profiles mentioned, a number of demands are made, in particular, on the matrix system of the dry chemical detection elements. Thus, in blood diagnosis tests in which the wiping-off of the excess of sample should be avoided, the removal of red blood cells must take place within the reagent matrix. The serum should diffuse into a further reagent layer and generate a color reaction with specific detection reagents there which is unaffected by erythrocytes.
In many cases, it is convenient or even necessary to embed the reagents needed for the detection spatially in separate layers. For example, in German Auslegeschrift 1,598,153, systems are described in which a permeable layer in the form of a plastic gauze, which, for example, can remove interfering ascorbic acid in a selective reaction, is connected to the reagent layer. The separate embedding of the detection reagents in different matrix layers is frequently of great advantage, in particular in complicated detection reactions which proceed in reaction cascades and require enzyme systems having different optimum pH ranges. In immunodiagnostic detection reactions, moreover, matrix layers which enable immobilization of antigens, antibodies, enzymes or other biological active substances, are additionally necessary.
Several developments have already been described for the preparation of detection systems of this type, which as a rule are based on a multilayer matrix structure. Thus, European Patent application 0,267,519 describes test carriers which essentially consist of glass fiber wadding for erythrocyte removal and a reagent layer composed of a microporous polymer film. However, the total system still requires a number of other auxiliary layers, so that for the total structure, depending on the detection reaction, seven or more individual layers are combined in a relatively complicated structure.
In addition to complicated production processes, the demands on precision are increasingly difficult to fulfill with an increasing number of individual layers fixed to one another.
German Patent Specification 3,922,495 describes diagnosis systems based on asymmetric membrane matrices which enable a plasma separation within the membrane layer and thus no longer have to be wiped off. For complicated detection reactions or with regard to an improved distribution of the sample on the application side, additional layers, such as special papers or waddings are also fixed there above the actual reagent matrix.
Multilayer integral analytical elements, in particular those based on gelatin films, have already been known for a relatively long time. Thus a typical diagnosis system as described in U.S. Pat. No. 3,922,158 consists, for example, of individual layers for carrier, reagent layer, reflection layer, filter layer and spreading layer. The preparation of multilayer gelatin films is best known from photography and presents no difficulties in terms of production technique. Further processing to give the diagnosis system also proceeds simply, since the multilayer systems can be handled as a film and several layers do not have to be laminated or glued one above the other in complicated processes as in the above-mentioned systems. However, a disadvantage of gelatin systems is that they are non-porous, swelling layers, so the physiochemical processes which are strongly temperature-dependent also occur in addition to the desired detection reaction during sample application.
For this reason, the gelatin systems mentioned only work accurately and reproducibly under thermostated conditions. The gelatin systems mentioned can thus only be employed in large-scale clinical equipment where the maintenance of defined temperature and moisture conditions is possible.
Multilayer, microporous membrane systems which are entirely integrated in one film are accordingly of particular interest for the future generation of diagnosis systems. The complicated laminating to one another of different layers would as a result become unnecessary. Systems of this type would combine the excellent properties of non-swelling polymer membranes which are adjustable with respect to porosity and chemical composition with the ability for simple further processing of multilayer gelatin films.